The invention relates to an electromedical apparatus, in particular, a current stimulation apparatus, comprising an output stage as the current waveform generator for constant-current stimulation current and comprising a protection installation, associated with the output stage, which disconnects the patient output from the operating voltage when a specifiable maximum value of the patient current is exceeded.
Known current stimulation apparatus have output stages for constant-current supply of patient current which operate with a relatively high operating voltage (up to several hundred volts). It is thus to be guaranteed that, even in the case of extremely high patient resistances, the currents with a correspondingly high operating voltage requirement, which are necessary for therapy or diagnosis, respectively, can still be applied.
Due to the high operating voltages connected to the patient, the danger could exist that, in the case of malfunction, the current flowing through the patient may assume dangerously high values. According to VDE-regulations, therefore, special protection installations are prescribed for all current stimulation apparatus and diagnosis apparatus which limit (or restrict) the patient current, in every possible instance, to I.sub.Patient &lt;80 mA.sub.eff.
From the German OS No. 2,749,792 (U.S. Pat. No. 4,200,108), a stimulation current apparatus is also known in which the protection installation is specially designed such that, in the case of increases in the patient current, brought about through rapid resistance changes, the operating voltage control unit of the apparatus is correspondingly downwardly controlled. This protection installation thus offers protection, in particular, for such an instance of malfunction in which the current supply electrodes become detached (or separated) from the application location, whereby the current transfer surface is reduced, so that the current density on the skin at the point of application can assume very high value and can thereby lead to unpleasant irritations. This protection installation is also effective against excessively rapid intensity changes resulting from too rapid operation of the intensity adjustment element. By contrast, this known circuit does not become engaged when the actually flowing patient current assumes an excessively high value due to apparatus errors, or the like. Current stimulation apparatus of the state of the art exhibits, for this purpose, so-called quick-acting safety fuses, for example, in the patient current circuit as a protection installation, which fuses are destroyed by correspondingly high currents and thus interrupt the current flow. Safety fuses of this type are, however, as is known, imprecise and also unsafe. Also, electromagnetic switching installations (relays) here bring about no fundamental improvements. Although they switch more rapidly (in the millisecond range), they are able to provide only protection against a specified excess current.